The invention relates to a display having at least one hand which can be driven by an electric drive, it being possible for the hand or the hands to execute rotations of more than 360xc2x0 in a first direction.
The prior art discloses, for example, displays of radio-controlled timepieces having a plurality of hands. These radio-controlled timepieces are controlled centrally via a longwave transmitter. If the reception of the long waves in the timepieces is disrupted, or following a battery change in such a timepiece, synchronization of the dial train is necessary. For this purpose, it is known to arrange, in gear wheels of the gear stages of the timepiece, perforated masks in the form of holes or through-passages in a defined form in the gear wheels, it being possible for these to be decoded by an optical sensor and thus likewise for the positions of the hands to be decoded.
The disadvantages here are the high tolerance requirements which have to be met for producing the perforated masks, small tolerances in assembly by the divergence of the production sizes, and necessary positioning accuracy of the optical sensors.
The object of the invention is thus to provide a display having at least one hand in the case of which, for at least one of the hands, a defined reference position can be detected without an optical sensor and the tolerance-related requirements can be lower.
These objects are achieved in that the hand or the hands can be rotated in a second direction which is counter to the first direction, in that the hand or one of the hands can be rotated in the second direction only up to a certain position and, in this certain position, assumes a reference position, and in that there is a detecting device which detects the inability to rotate further in the second direction.
In a particularly straightforward manner, the hand or one of the hands can be prevented from rotating further beyond a certain reference point in a second direction by a stopping device.
A straightforward configuration of the stopping device can be realized in that one or more locking bars are mounted such that they allow unlimited rotation in the first direction similar to a freewheeling hub, for example, of a bicycle and interact with a stop upon rotation in the second direction and thus prevent further rotation of the hand or of the hands.
In an even more straightforward and inexpensive manner, the stop device can be realized in that it has one or more segments which interact in each case with a stop, it being the case that the segment or the segments or the stop or the stops is/are mounted such that they can be rotated about an axis of rotation and the segments have slanting surfaces which, upon rotation of the hand in the first direction cause an axial displacement of the segment or of the segments or of the stop or of the stops such that the rotation can be continued in an unlimited manner, and it being the case that, upon rotation in the second direction, the segment or the segments strikes or strike in a certain position against the stop or the stops and thus rules or rule out further rotation in the second direction, and the hand is connected in a rotationally fixed manner to the segment or the segments or the stop or the stops.
A plurality of segments at different distances from the axis of rotation achieve the situation where each segment can only interact with a certain stop and can thus assume a reference position during rotation. Due to the plurality of such segments which are arranged around the axis of rotation, canting of the components is ruled out by the axial movement of the segment and stop with respect to one another, by the uniform development of force of all the slanting surfaces of the segments.
The arrangement of a plurality of segments can be realized particularly favorably on a first disk, it being possible for the component to be configured as a single-piece injection molding from segments and disks. It is likewise possible for the stops to be arranged particularly favorably on a second disk.
Installation is particularly straightforward if one of the two disks is configured as part of a housing of the display or of the drive thereof. A detecting device which detects the inability of the hand to rotate further in the second direction can be realized via monitoring of the power consumption of the electric drive. As soon as the hand has reached its reference position, upon rotation of the hand in the second direction, and cannot move any further in the second direction, the power consumption of the still switched-on electric drive increases considerably, with the result that, by monitoring the power consumption, it is possible to infer, for a considerably increased value, that the reference position has been reached.
If the electric drive has a permanent-magnet rotor and a plurality of coils which are supplied with power one after the other, for example, in the manner of a stepping motor and thus move the permanent-magnet rotor further, it is possible, by monitoring the voltages which the permanent-magnet rotor induces, by its movement, in a coil which has not been supplied with power, to infer the rotation of the rotor. Accordingly, if it is no longer possible to establish any induced voltage, it is thus detected that the hand has assumed its reference position.